There is an AC-DC conversion device that converts alternating current power into direct current power or direct current power into alternating current power. The AC-DC conversion device includes multiple switch portions (thyristor valves) having a bridge connection and converts the alternating current power into the direct current power or the direct current power into the alternating current power by controlling the ON timing of each of the switch portions. For example, a separately-excited switching element such as a thyristor or the like is included in each of the switch portions. Also, in the AC-DC conversion device, the voltage value and the current value of the direct current power can be controlled by controlling the timing of the triggering of each of the switch portions.
For example, the AC-DC conversion device controls the ON timing of each of the switch portions by AVR control (Automatic Voltage Regulator: constant voltage control) that causes the voltage value of the direct current voltage to be a substantially constant voltage value corresponding to a prescribed voltage command value.
For example, the AC-DC conversion device is used in a direct current power transmission system that performs power transmission by converting alternating current power into direct current power. In the direct current power transmission system, the AC-DC conversion device is connected to a direct current circuit such as a direct current cable, etc., converts the alternating current power of a connected alternating current circuit into direct current power, and supplies the direct current power to the direct current circuit. Or, the AC-DC conversion device converts the direct current power of the connected direct current circuit into alternating current power and supplies the alternating current power to the alternating current circuit.